/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.nutch.util;

import java.io.IOException;

import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.MapFile;
import org.apache.hadoop.io.SequenceFile;

/**
 * Utility methods for common filesystem operations.
 */
public class FSUtils {

	/**
	 * Replaces the current path with the new path and if set removes the old
	 * path. If removeOld is set to false then the old path will be set to the
	 * name current.old.
	 * 
	 * @param fs
	 *            The FileSystem.
	 * @param current
	 *            The end path, the one being replaced.
	 * @param replacement
	 *            The path to replace with.
	 * @param removeOld
	 *            True if we are removing the current path.
	 * 
	 * @throws IOException
	 *             If an error occurs during replacement.
	 */
	public static void replace(FileSystem fs, Path current, Path replacement,
			boolean removeOld) throws IOException {

		// rename any current path to old
		Path old = new Path(current + ".old");
		if (fs.exists(current)) {
			fs.rename(current, old);
		}

		// rename the new path to current and remove the old path if needed
		fs.rename(replacement, current);
		if (fs.exists(old) && removeOld) {
			fs.delete(old, true);
		}
	}

	/**
	 * Closes a group of SequenceFile readers.
	 * 
	 * @param readers
	 *            The SequenceFile readers to close.
	 * @throws IOException
	 *             If an error occurs while closing a reader.
	 */
	public static void closeReaders(SequenceFile.Reader[] readers)
			throws IOException {

		// loop through the readers, closing one by one
		if (readers != null) {
			for (int i = 0; i < readers.length; i++) {
				SequenceFile.Reader reader = readers[i];
				if (reader != null) {
					reader.close();
				}
			}
		}
	}

	/**
	 * Closes a group of MapFile readers.
	 * 
	 * @param readers
	 *            The MapFile readers to close.
	 * @throws IOException
	 *             If an error occurs while closing a reader.
	 */
	public static void closeReaders(MapFile.Reader[] readers)
			throws IOException {

		// loop through the readers closing one by one
		if (readers != null) {
			for (int i = 0; i < readers.length; i++) {
				MapFile.Reader reader = readers[i];
				if (reader != null) {
					reader.close();
				}
			}
		}
	}
}
